This proposal addresses the feasibility of developing an easy-to-use, low cost, personal biosensor for serum creatinine, a critical indicator of renal function. A personal creatinine sensor would enable kidney transplant patients to monitor the health of their transplanted kidney in the home environment. The sensory design consists of two parts; a test ship which contains all the biochemistry in a dry format and a compact, inexpensive instrument to read and store the test results. The instrument is currently under in house development for application to other analytes including ATP, galactose, and phenylalanine. This Phase I proposal focuses on the biochemistry of the creatinine bioluminescence-based biosensor. The test strip can be conceptually divided into two "reaction zones", i.e., a sample pre-treatment zone and a signal transduction zone. The biochemistry involves the conversion of creatine to creatine. Creatine is then phosphorylated by the enzyme creatine kinase with the simultaneous consumption of ATP. Unused ATP is the quantified via the firefly-luciferase reaction which produces light that is measured in the instrument. The result is a two channel device which measures both creatine and creatine and will be applicable to both blood and urine samples. PROPOSED COMMERCIAL APPLICATIONS: Routine, creatinine monitoring is a creatinine is an early predictor of transplant rejection and a subsequent kidney failure. There are fifty to sixty thousand transplant patients who would benefit from weekly monitoring of their serum creatine. At $10 per assay this is a $25-$39 million gross annual market.